1. Field of the Invention
The present invention relates to a patterned substrate and a method and apparatus for manufacturing the same.
2. Description of the Background Art
Recently, high resolution, high image quality display devices with reduced display unevenness such as reduced luminance unevenness, reduced color unevenness and the like have been increasingly demanded. Such a demand has raised a need for improved accuracy of a patterned substrate such as a color filter substrate and an organic electroluminescent substrate. A color filter substrate is a substrate which is used in display devices such as a liquid crystal display (LCD) and an electroluminescent display using a color filter. An organic electroluminescent substrate (hereinafter, sometimes referred to as “organic EL substrate”) is a substrate which is used in an organic electroluminescent display (hereinafter, sometimes referred to as “organic EL display”).
Examples of a method for manufacturing a patterned substrate include a dyeing method, a pigment dispersion method, an electrodeposition method, a vacuum deposition method, a spin coating method, a dip method, a roll coating method, a doctor blade method, an ink jet method, and the like.
In the ink jet method, a matrix pattern can be relatively easily formed as compared with other methods for manufacturing a patterned substrate. Moreover, in the ink jet method, a manufacturing process is relatively short and a patterned substrate can be manufactured at low cost. The ink jet method has therefore attracted attention as a method for manufacturing various kinds of patterned substrate (for example, Japanese Laid-Open Patent Publication No. 10-12377).
In the ink jet method, a patterned substrate is formed by ejecting ink from an ink ejecting nozzle of an ink jet head to each of a plurality of ink ejection portions arranged in a matrix while scanning a substrate with the ink jet head, and then drying the ejected ink into a solid state.
For improved production efficiency, an ink jet head having a plurality of ink ejecting nozzles is usually used in the ink jet method to eject ink simultaneously to a plurality of ink ejection portions arranged in a row.
In order to improve placement accuracy of ink which is ejected from ink ejecting nozzles and to prevent mixing of ink which has been ejected to adjacent ink ejection portions, there has been proposed a technique for separating a plurality of ink ejection portions from each other by an ink-ejection-portion formation layer having a liquid repelling property (an ink repelling property) (for example, SID Digest 1999, pp. 376-379).
However, when ink is ejected simultaneously to a plurality of ink ejection portions arranged in a row by using an ink jet head having a plurality of ink ejecting nozzles, an ink layer formed in an inner part of the row (hereinafter, sometimes simply referred to as “inner part”) and an ink layer formed in end parts of the row (hereinafter, sometimes simply referred to as “end parts”) have different thicknesses (MRS BULLETIN/NOVEMBER 2003, pp. 821-827).
Hereinafter, the reason why ink layers in an inner part and end parts of a row have different thicknesses will be described in detail.
FIG. 6 is a schematic plan view illustrating the step of ejecting ink to ink ejection portions 307 on a main substrate 301 (not shown in FIG. 6) by a conventional ink jet method.
FIG. 7 is an enlarged schematic cross-sectional view taken along line VI-VI in FIG. 6.
FIG. 8 is a schematic cross-sectional view of the main substrate 301 having ink layers 308 formed thereon by the conventional ink jet method.
FIG. 9 is an enlarged cross-sectional view of a portion surrounded by dotted line VIII in FIG. 8.
For convenience, in FIGS. 8 and 9, the thickness of ink layers 308 relative to a bank 303 is shown to be larger than their actual thickness. Actually, the bank 303 is about 1 μm to about 5 μm high and the ink layers 308 are about 10 nm to about 200 nm thick.
A plurality of ink ejection portions 307 arranged in a matrix are formed on the main substrate 301. The plurality of ink ejection portions 307 are separated from each other by the bank 303. A light shielding layer 302 is formed between the main substrate 301 and the bank 303. A region of each ink ejection portion 307 in which the light shielding layer 302 is not formed is an effective region PD3. Note that an “effective region” is a region which is to be actually used as a device. For example, provided that a patterned substrate is a color filer substrate or an organic EL substrate, an “effective region” refers to a display aperture region.
The ink layers 308 are formed by ejecting ink droplets 304 to the ink ejection portions 307 on the main substrate 301 by using an ink jet head 306 and drying the ink droplets 304 which have been ejected to the ink ejection portions 307 into a solid state. The ink jet head 306 has a plurality of ink ejecting nozzles 305. The plurality of ink ejecting nozzles 305 are provided corresponding to a plurality of ink ejection portions 307 arranged in a row. The plurality of ink ejecting nozzles 305 can thus eject ink droplets 304 simultaneously to a plurality of ink ejection portions 307 arranged in a row. Ink droplets 304 are ejected to a plurality of ink ejection portions 307 arranged in a matrix in a target block B3 while scanning the main substrate 301 in the Y-axis direction with the ink jet head 306. The ink jet head 306 is then moved by one block B3 in the X-axis direction, and ink droplets 304 are similarly ejected to a plurality of ink ejection portions 307 in the next target block B3 while scanning the main substrate 301 in the Y-axis direction with the ink jet head 306.
A patterned substrate is thus produced by ejecting ink droplets 304 to all the ink ejection portions 307 while scanning the main substrate 301 in the Y-axis direction with the ink jet head 306 a plurality of times. Note that a block B3 is a region of the main substrate 301 in which the ink layer 308 can be formed on each ink ejection portion 307 each time the main substrate 301 is scanned in the Y-axis direction with the ink jet head 306.
By using the ink jet head 306, ink droplets 304 are ejected to the ink ejection portions 307 on a block B3 by block B3 basis. In this case, when the ink droplet 304 dries into a solid state, a vapor pressure of a volatile component of ink in the periphery of an ejected ink droplet 304 is different between an inner part S and end parts E of the block B3. In general, the vapor pressure of the volatile component of ink is uniform in the inner part of the block B3. In the end parts of the block B3, however, the vapor pressure of the volatile component of ink becomes lower toward both ends of the block B3. Ink droplets 304 therefore dry at a different rate between the inner part S and the end parts E. As a result, the shape of the ink layer 308 is different between the inner part S and the end parts E.
Conventionally, a solid content weight of ink which is ejected to each ink ejection portion 307 is approximately the same. Therefore, if the shape of the dried ink layer 308 is different, the thickness in the effective region PD3 of the ink layer 308 is also different. Accordingly, the ink layers 308 formed in the inner part S have approximately the same thickness H7, while the ink layers 308 formed in the end parts E become thinner toward the ends of the block B3. For example, as shown in FIG. 9, the thickness H7 of the ink layers 308 in the inner part S and thicknesses H8 and H9 of the ink layers 308 in the end part E become smaller in this order.
In FIGS. 8 and 9, the ink layers 308 in the end parts E have a concave shape. However, the ink layers 308 in the end parts E need not necessarily have a concave shape. The ink layers 308 in the end parts E may have a more convex shape than that of the ink layers 308 in the inner part S depending on manufacturing conditions.
In FIGS. 8 and 9, only two ink layers 308 in each end part E are shown to have a different shape from that of the ink layers 308 in the inner part S. Depending on manufacturing conditions, however, only one ink layer 308 or three or more ink layers 308 in each end part E may have a different shape from that of the ink layers 308 in the inner part S.